Resistance type detector



Dec. 24, 1946. H. WOLFSON ET AL RESISTANCE TYPE DETECTOR Filed April 17, 1943 J2) Inventor I Attorney Patented Bee. 24, 1946 arisen 2,413,021 7 RESISTANCE TYPE nn'rno'ron Henry Wolfson and Stanley Garden Shepard,

London, England, assignors, by mesne assignments, to International Standard Electric Corporation, New York, N. Y., a corporation of Delaware Application April 17, 1943, Serial No. 483,522

In Great Britain May 22, 1942 2 Claims.

This invention relates to resistance elements for electric circuits, and particularly to those elements known as thermistors which have a very high temperature coefilcient of resistance,

Thermistors have been in use for some years and are characterised by a temperature coeflicient of resistance which may be either positive or negative and which is moreover many times the corresponding coefiicient for a pure metal such as copper. This property renders thermistors particularly suitable for a variety of special applications in electric circuits.

Various difierent materials are available for the resistance element of a thermistor, these various materials having difierent properties in other respects; as one example, a resistance material having a high negative temperature coefficient of resistance comprises a mixture of manganese oxide and nickel oxide, with or Without the addition of certain other metallic oxides, the mixture being suitably heat treated.

Thermistors have been employed in two different forms: (a) known as a directly heated thermistor and comprising a, resistance element of the thermally sensitive resistance material provided with suitable lead-out conductors or terminals, and (1)) known as an indirectly heated thermistor comprising the element (a) provided in addition with a heating coil electrically insulated from the element. A directly heated thermistor is primarily intended to be controlled by the current which flows through it and which varies the temperature and also the resistance accordingly. Such a thermistor will also be afiected by the temperature of its surroundings and may therefore be used for thermostatic control and like purposes with or without direct heating by the current flowing through it. An indirectly heated thermistor is chiefly designed to be heated by a controlling current which flows through the heating coil and which will usually, but not necessarily, be different from the current which flows through the resistance element; but this type of thermistor may also be subjected to either or both of the types of control applicable to a directly heated thermistor.

More detailed information on the properties of thermistors will be found in an article by G. L. Pearson in the Bell Laboratories Record Dec. 1940, page 106.

The present invention relates to the construc tion of directly or indirectly heated thermistcrs suitable for use at ultra high frequencies where the wave length is of the order of a few centimeters. The leads carrying the currents for controlling the thermistor are arranged as a dipole antenna for receiving the short waves and applying them directly to the thermistor. The arrangement provides, for example, a simple and accurate means of measuring the field strength, or with a suitable type of resistance element, could be adapted as a detector.

According to the invention there is provided a thermistor for measuring and/or detecting ultrahigh frequency electromagnetic Waves, comprising a resistance element having a high temperature coeflicient of resistance assembled inside an elongated glass bulb, and a pair of straight conductors passing outside the bulb at opposite ends for leading the waves to the thermistor, the said conductors being arranged in a straight line to form a dipole antenna, the lengths of the conductors being adjusted in accordance with the incoming wavelength.

The invention will be more clearly understood from the following detailed descriptionof two embodiments with reference to the accompanying drawing in which:

Fig. 1 shows a directly heated thermistor; and

Fig. 2 shows an indirectly heated thermistor, both according to the invention.

Fig. 3 is an enlarged view of the thermistor element of Fig. 2.

The first embodiment of the invention is shown in Fig. 1. It shows a directly heated thermistor bead l assembled in a cylindrical glass bulb 2. This bead may comprise, for example, a resistance element consisting of thermally sensitive material mounted on fine wires 1 and 8 similar to that shown in Fig. 1 of the specification of United States Patent No. 2,282,944, dated May 12, 1942. The lead-out conductors 3 and 4 for the resistance element are arranged in the same straight line and are sealed through corresponding presses 5 and 6 at opposite ends of the bulb 2. The fine wires I and 8 are welded to the lead-out conductors 3 and 4 in the manner indicated so as to support the bead I. This operation may be con,- veniently done with the help of a suitable jig for holding the parts together in the proper positions.

The bulb 2 may conveniently be made from a short length of glass tubing and may be arranged to be slipped over the bead assembly while on the jig, and may be scaled down onto the lead-out conductors 3 and 4 formin the corresponding presses 5 and 6.

An indirectly heated thermistor arranged as a dipole is shown in Fig. 2 and Fig. 3. The bead H is in this case provided with a heating coil l6 and may, for example, be generally similar to that shown and described in connection with Figs. 1 and 2 of U. S. patent specification No. 2,280,257 or in the specification of patent in Great Britain No. 449,352 filed July 4, 1942. The bulb l2 which encloses the bead II is similar to the bulb 2 shown in Fig. 1 but has a short side tube symmetrically placed and provided with a press l3. In this case, the lead-out conductors 9 and ID for the heating coil are arranged in line to form the dipole antenna and pass out of the bulb through the presses 5 and 6. The lead-out conductors 3 and 4 from the resistance element are arranged parallel to one another and pass out of the bulb through the press l3 at right angles to the leads 9 and Ill. The parts will preferably be assembled in a, suitable jig by Welding or otherwise fixing the wires l4 and I5 of heating coil IE to the leads 9 and I0, and then slipping the bulb l2 over them and sealing as described in connection with Fig. l. The resistance element IT, as shown in Fig. 3 may then be mounted on the conductors 3 and 4 by welding or otherwise fixing the wires 1 and 8 thereto and may be coated with a suitable liquid cement. It may be then slipped through the side tube of the bulb 12 into the heating coil l6 so as to be correctly placed, and the press 13 finally sealed down onto the conductors 3 and 4.

In the case of either embodiment of Fig. 1 or 2, the bulb may be filled with an inert gas before sealing, or if preferred, a small side tube may be provided for exhausting the bulb in the usual Way.

It will be noted that the dipole antenna is formed by the resistance element leads in the case of Fig. 1 and by the heating coil leads in the case of Fig. 2. In either case, of course, these leads will be cut to a suitable length having regard to the wave length which it is desired to employ.

As an illustration, the resistance element might be 0.02 inch diameter and the fine supporting Wires might be platinum wires about 0.002 inch or without the addition of certain other metallic oxides, in which case it would have a negative temperature co-efficient of resistance. These details have been given merely as examples and not as limitations, and it will be evident that such details will be appropriately chosen With the requirements of each particular case.

What is claimed is:

1. A device for detecting ultra high frequency electromagnetic waves, including a resistance element having a high temperature co-efficient of resistance, an elongated bulb havving said element located therewithin, lead Wires connected to said element and extending through the walls of said bulb at one side thereof, also including a heating coil mechanically integral with said element but electrically discrete therefrom, a pair of straight conductors forming leads to said heating coil and passing outside the bulbat opposite ends thereof for leading the waves to the device, said conductors being arranged in a straight line to form a dipole antenna, the lengths of the conductors being adjusted in accordance with the incoming wavelength, whereby electrical coupling between said lead Wires and said pair of conductors is minimized.

2. A device according to claim 1, in which HENRY VVOLESON. STANLEY GARDEN SHEPARD. 

